Observed suppression of room temperature negative differential resistance in organic monolayers on Si(100)

Abstract

The ultrahigh vacuum scanning tunnelling microscope was used to probe charge transport through two different organic monolayers adsorbed on the Si(100) substrate at room temperature. I–V measurements were taken on monolayers of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and cyclopentene for degenerately doped n-type and p-type substrates. Initial I–V measurements for transport through the TEMPO monolayer exhibited a suppression of negative differential resistance (NDR) relative to previously reported charge transport through isolated molecules. I–V measurements were also performed on isolated cyclopentene molecules and cyclopentene monolayers. Similarly to TEMPO monolayers, the cyclopentene monolayers exhibited attenuated NDR behaviour relative to isolated molecules. The observed NDR suppression suggests that the high packing density of organic monolayers influences charge transport through molecule–semiconductor junctions.

Probing charge transport at the single-molecule level on silicon by using cryogenic ultra-high vacuum scanning tunneling microscopy

“…2b is a consecutive series of four current-voltage measurements taken over an isolated cyclopentene molecule at 80 K, where the sweep direction of the voltage alternated between each curve. Each of the curves shows clear NDR at positive sample bias, in agreement with previous observations at room temperature (29)(30)(31). Immediately preceding NDR, a peak is observed in the current-voltage curve, which corresponds with the optimal resonant tunneling condition.…”

“…Fig. 2a is a typical current-voltage measurement taken over the clean Si(100)-2ϫ1 surface at 80 K. The current-voltage curve shows no NDR and agrees with expectations for a semiconductor-vacuum-metal tunnel junction (30). Assuming a onedimensional tunnel barrier, the tip-sample spacing on the clean Si(100)-2ϫ1 surface is estimated from this current-voltage curve to be Ϸ10 Å.…”

“…We have previously reported the study of charge transport through organic molecules covalently bound to silicon surfaces with room-temperature UHV STM (29)(30)(31). These initial experimental studies revealed doping-dependent unipolar negative differential resistance (NDR) in the current-voltage curves on individual molecules.…”

Progress with Molecular Electronic Junctions: Meeting Experimental Challenges in Design and Fabrication

“…[33] In a different STM investigation, it was demonstrated using a three-terminal single-molecule device that the electric field from a charged surface atom could modulate the conductance of nearby molecules bonded to a silicon surface. [23] Unique behavior, such as negative differential resistance, has been reported for single molecules on silicon, [87,100] consistent with a theoretical model based on alignment of the molecular orbital energies with those of the semiconductor. [101] In addition to a strong Si-C bond in many of the single-molecule experiments on Si, the interactions of the molecular energy levels with the semiconductor bands in Si can be exploited to achieve useful electronic effects.…”

A comparative study of electron transport in benzene molecule covalently bonded to gold and silicon electrodes for pioneering the electron transport properties of silicon quantum dot-molecule hybrid polymers

“…In particular, Ratner group published a model paper that theoretically describes the electron transport properties in molecular junctions with the semiconductor electrodes by analytically accounting for the onedimensional moleculeeelectrode interactions [38]. On the other hand, most of other studies were dealing with the electron transport properties of molecules in semiconductor-molecule-metal, socalled heteroelectrode junctions, which describe experimental measurement on Si substrate with a metal tip in the use of scanning tunneling microscope (STM) [34,43], and demonstrated that the negative differential resistance (NDR) from the molecular junction of the semiconductor-molecule-metal structure arises from the combination of discrete molecular orbital energy and band gap nature of the Si semiconductor electrode [39,40].…”